GPS Antenna Testing

by David Dunning

GPS stands for Global Positioning System. A group, or constellation, of satellites orbiting more than 12,000 miles above the surface of the Earth sends radio frequency signals to GPS ground stations consisting of a receiver and an antenna.

Signal Degradation

When a GPS signal is transmitted from a satellite to an antenna on the ground, it suffers degradation. This can be caused by refraction and absorption in the atmosphere, reflection from trees or buildings, or deliberate or accidental jamming.

Low Noise Amplifier

GPS antennae typically consist of an antenna assembly and a lo- noise amplifier. The low noise amplifier is often a semiconductor chip made from gallium arsenide; it is sensitive to voltage and the power level required to destroy it is very low. If you attempt to measure the impedance or resistance at the antenna connector, you may damage the low-noise amplifier irreparably.

Receiver

A GPS antenna cannot be tested effectively unless it is connected to a receiver. Simply connecting an antenna to a spectrum analyzer -- a device that generates a signal and tests the signal reflected by the antenna -- is not sufficient to diagnose problems.

About the Author

A full-time writer since 2006, David Dunning is a professional freelancer specializing in creative non-fiction. His work has appeared in "Golf Monthly," "Celtic Heritage," "Best of British" and numerous other magazines, as well as in the book "Defining Moments in History." Dunning has a Master of Science in computer science from the University of Kent.